Field of the Invention
The present invention generally relates to charge transfer.
Description of Related Art
Persons of ordinary skill in the art understand terms and basic concepts related to microelectronics that are used in this disclosure, such as “voltage,” “signal,” “logical signal,” “clock,” “phase,” “capacitor,” “charge,” “current,” “transistor,” “MOS (metal-oxide semiconductor),” “PMOS (p-channel metal oxide semiconductor),” “NMOS (n-channel metal oxide semiconductor),” “source,” “gate,” “drain,” “threshold voltage,” “circuit node,” “ground node,” “operational amplifier,” “virtual ground,” “electrical potential,” “switch,” “open circuit,” “short circuit” “single-ended circuit,” and “differential circuit.” Terms and basic concepts like these are apparent to those of ordinary skill in the art and thus will not be explained in detail here.
Through this disclosure, a logical signal is a signal of two states: “high” and “low,” which can also be re-phrased as “1” and “0.” For brevity, a logical signal in the “high” (“low”) state is simply stated as the logical signal is “high” (“low”), or alternatively, the logical signal is “1” (“0”). Also, for brevity, quotation marks may be omitted and the immediately above is simply stated as the logical signal is high (low), or alternatively, the logical signal is 1 (0), with the understanding that the statement is made in the context of describing a state of the logical signal.
A logical signal is said to be asserted when it is high. A logical signal is said to be de-asserted when it is low.
A clock signal is a cyclic logical signal. For brevity, hereafter, “clock signal” may be simply referred to as “clock.”
FIG. 1 shows a schematic diagram of a prior art charge transfer circuit 100, which comprises: a first capacitor CI, a second capacitor CF, and an operational amplifier 110. The operational amplifier 110 imposes a virtual ground condition on a circuit node 101, thus causing a charge stored on the first capacitor CI to transfer to the second capacitor CF. The principle of the prior art charge transfer circuit 100 is well known to those of ordinary skill in the art and thus not explained in detail here. An issue with the prior art charge transfer circuit 100 is: the operational amplifier 110 needs to provide an output current IO injected to the circuit node 101 via the second capacitor CF to impose the virtual ground condition on the circuit node 101 and thus fulfill the charge transfer. To enable a fast charge transfer, the operational amplifier 110 should have a high driving capability, which enables a large output current IO. An operational amplifier of a high driving capability is power hungry. Therefore, the prior art charge transfer circuit 100 is power hungry if a fast charge transfer is sought.
What is desired is a charge transfer circuit that is more power efficient.